Once again the Federal Election Commission has asked the Republican non-profit group Crossroads GPS to disclose its donors.

And once again the big-spending organization linked to Karl Rove has rebuffed the request.

The latest back-and-forth began yesterday, when the FEC sent Crossroads GPS a formal Request For Additional Information (RFAI) asking about its fourth-quarter 2012 report showing more than $50 million in independent expenditures aiding Republican candidates — but no donations.

Donors giving more than $200 “to further the independent expenditures” must be itemized on the documents, FEC campaign finance analyst Christopher Whyrick wrote to Crossroads GPS. “Please amend your report to provide the missing information.”

Echoing its responses to similar FEC requests in 2011 and 2012, Crossroads GPS says it doesn’t have to disclose donations because they weren’t solicited or received specifically to “further” the independent expenditures.

The Republican group’s latest response was swift and direct.

“Your continued RFAIs on this subject are unnecessary,” Crossroads GPS treasurer Caleb Crosby wrote to the FEC today. “However, if you are required by Commission guidelines or procedures to continue to send them, we will continue to respond with the exact same explanation.”